Method of making optical lines in dielectric body

ABSTRACT

A PRINTED OPTICAL CIRCUIT INCLUDING A TRANSPARENT DIELECTRIC BODY ON WHICH AT LEAST ONE ELONGATED REGION IS FORMED. A VARYING REFRACTIVE INDEX IS ESTABLISHED IN THE DIELECTRIC BODY BY VARYING THE RELATIVE CONCENTRATION OF METALLIC POSITIVE IONS THEREIN. A METHOD FOR FABRICATING THE OPTICAL CIRCUIT IS ALSO DESCRIBED.

Patented .inne iii? lvtETHOli) Ol? M ilst? GPTECL Libia@ IN BELLLC @BYUchida, C/o Nippon ectric Company, Ltd., '-S

oa Gochorne, iv atofltu, Tokyo, 4iapan Ter Continuation-innpart ofabandoned application Ser. No.,

10H/"53, Dec. 7.8, 1970. ',...ris :application Sept, 26, i972, Ser. No.29?.,3tl5

Claims priority, application apnn, Dec. 29, 1969, iS/Ittidl lint. Cl.Ctlc 15/00 US. Cl.

65-36 il@ Claims metallic positive ions therein. A method forfabricating the optical circuit is also described.

This application is a conti nuation-in-part of application er. No.101,743, tiled Dec. 2S, i970, and now abandoned.

The present invention relates generally to optical cir cuits, and moreparticularly to the construction of a printed type optical circuit.

The field of opt0-electronics, which combines light and electricaltechniques, has recently been developed. While improvements inminiattu'ization have been achieved from the usevoi printed circuits tothe use of integrated circuits in the field of electric circuits, theachieving of'increased miniaturization has heretofore not been developedto any appreciable degree in the field of circuits employing light.There thus exists an imbalance between optical circuits and electriccircuits with respect to their rnaufacture and the minimum size of theapparatus that can be achieved.

For instance, although an electric connection between a light signalsource, such as an electro-lurninescent diode, a photo-electrictransducer element, such as a photodiode, and other circuit elements canbe realized relatively easily in a compact form as by a printed circuitor the like, if the optical transmission lines connected between theelectroluminesccnt diodes and the photo diodes are formed byconventional optical fibers such as, for instance, glass fibers, it isthen necessary to connect individual independent glass fi ers betweenthe respective elements. The number of operations required in thisprocess is extremely high, and, therefore, facility of manufacture andhigh miniaturization cannot be expected.

A` glass fiber having a refractive index distribution, where therefractive index decreases gradually from the center axis towards theperiphery, is disclosed in cepending application, Ser. No. M1256, filedMay 26, 1S71, cntitled i-ibrous Coin/erging Light Guide Element. Thefocusingl light propagating medium disclosed in said applicaton(identified by the registered trade name, Selfoc) enables therealization of a rod lens having a minute aperture or a tlexibie lens asexplained on pp. 24 and 25 of Japan Electro/zic Engineering, February1969, and thus enables the realization of the so-called micro-optics"effect. However, even with this focusing light propagating medium, thenumber of fabrication operations required to produce the desired numberof conducting paths is still relatively large. ln an attempt' toimprovel the conipnmms of such optical circuits, an integrated compactoptical circuit hus been proposed by S. E. Miller in RSTI, Septernber1969. 'fh-.11 circuit, while being, Somewhat more contpact than the reviously known optical circuits, is relatively diiiicult topracti/.zcily manufacture,

Uing at least one or Vmorey It is thus an object of the presentinvention to provide an improved printed optical circuit which may bemore readily fabricated than optical circuits that have heretofore beenknown to the prior art.

The pressptio dielectricbodyjcontauna@a I ity of 4metal ions. Anelongated region or regions are provided in tl dielectric body accordingto a desired pattern, in a manner such that the proportion or relativeconcentration of metallic positive ions in the body varies radiallyoutwardly from the center axis of the body. The refractive index of; thebody gradually decreases from the center axis radially outwardly, theelongated region or regions thus providing an optical transmission lineor lines.

In another aspect of the invention, a planar transparent body may bejoined to another' planar body, the proportion of positive ions in. thedielectric body varying along a transverse cross-section of thedielectric body from one or more points in the proximity or the joiningsurface in the direction away from the joining surface. An elongatedregion or regions, having a cross-section in which the rcfractive indexvaries gradually from the one or more points in the direction away fromthe joining surface, is formed according to a desired pattern to providean optical transmission line or lines. IE desired, channels that tend onboth sides of: each elongated region may be pro vided in the opticalcircuit.

Another feature of the present invention is a method for making adesired pattern of optical lines in a dielectric body, such as in thefabrication of the printed optical circuit described above. 'llhalmetbodincludes the step" of preparing ajplanar transparentydiclectric bodycontainv Y y u l indsof metallic positive ions, and for naga desiredpattern lor masken one surface of the transparcntwdielec ric ,."wsilt ofpositive metah lic ions having a larger iuic'polarizability per unitvolume (or electronic polarizability/ionic radiusB) than the metallicpositive ions contained in the dielectric body, is brought in Contactwith the transparent dielectric body through the mask to perform ionexchange. 'lfhe masi; is thereafter removed and a salt of metallicpositive ions having a smaller ionic polarizability per unit volume thanthe metallic positive ions used in the preceding step is brought incontact with the surface of the dielectric body to carry out ionexchange. 'lf desired, another body may then be joined onto the entiresurface of the. dielectric body.

The method of the present invention may also include the step of etchingthe part of the dielectric body exposed through the mask to apredetermined depth to form a predetermined pattern of elongated ridgeportions on the surface of the dielectric body prior to the removal ofthe mask. A salt of metallic positive ions having a lower ionicpolarizability than the metallic positive ions con tained in thedielectric body, is then brought into Contact with at least the surfaceportion corresponding to the ridge portion among the peripheral surfaceof the ridge portion and the surface opposite to the surface having theridge portion to carry out ion exchange. lf desired, another body may bejoined to the dielectric body on the surface opposite to the surface ofthe dielectric body on which the ridge portion is formed.

According7 to the present invention, since a Jredete:- mincd wiringl ofun optical circuit can be realized by viding a printed type of opticalcircuit having a r. termined wiring pattern, the wiring of a complexoptical circuit may he achieved through a single step, und 1' by massproduction of optical circuit apparatus is available.

To the accomplishment of the above and to such funy ther objects as mayhcreinatcr appear, the presen int/cm nt invention in one aspectA thereofprovides e tion relates to a printed type of optical circuit and methodfor making the same, substantially as defined in the appended claims andas described in the following specification taken ,together with theaccompanying drawings in which:

FIG. 1 is a perspective vier' of the essential part of an opticalcircuit according to a preferred embodiment of the present invention;

FIG. 2 is a crosssectional view taken along line 2 2 in FIG. 1;

FIGS. 3a and 3b are respectively a perspective view and a diagrannnaticview of a second embodiment of the invention; and

FIGS. litl-d and PIG. 5, respectively, show still other embodiments ofoptical circuits according to the present invention.

The essential part of a printed optical circuit according to the presentinvention, as shown in FIG. l, comprises a glass plate 1. A pair ofchannels 2 are etched on Athe surface of glass plate l and define anoptical line 3 according to a predetermined pattern as defined by theetched channels 2. A body d is joined onto the back sur face of glassplate 1 and has a refractive index that is lower than that of glassplate l. The optical line 3 is subjected to an ion exchange processing,in a manner more completely described in a later part of theapplication, so that its refractive index decreases from its innerportion towards its surface.

"MAS a result, a light projected into the optical line 3 along thedirection of its optical axis advances through optical line 3 whileoscillating. Even if the optical line is curved, the light can advancethrough optical line 3 along its curve.

It is known theoretically that if the refractive index of a lightpropagating body decreases from its center axis towards its periphery,then the light advancing in that body will he confined to within thelight propagating body, and will follow an optical line oscillatingaround the optical axis` ofthe light propagating' body. (For instance,reference is made to an article by S. E. Miller published in The BellSystem Technical Journal, November 1965.) It is also known that at theboundary between two bodies having different refractive indices, lightcoming through one of the bodies is reflected at the incident point tothe other body.

Therefore, the light projected into optical line 3 does not escape fromthe surface of optical line 3 as a result of the established refractiveindex gradient, and does not escape from the bottoni of the optical lineas a result of the reflection at the contact surface of optical line 3with body Accordingly, the light incident on optical line 3 advancesalong that line.

Therefore, optical line 3, provided in a predetermined pattern, can beutilized to optically connect between optical elements provided at theincident and emitting ends of the line, respectively. In other words,optical wiring can be achieved by the use of the optical circuit ofFIG. 1. Furthermore, in the embodiment of FIG. 1, since the necessarynumber of optical wiring leads can be formed on a single glass plate (bythe method of manufacture described below), an optical circuit providingoptical connections between many optical elements can be fabricatedthrough a single step.

in the fabrication of the optical circuit of FIG. 1, a thin glass plate1 having; a fixed refractive index and containing tivo or more modifyingoxides is prepared. A predetermined pattern of mask (Not shown) isprovided on the glass plate, and the latter is then etched by means of,for example, hydrotinoric acid. As a result of the etching, channels 2as well as the ridge portions 3 defined by channels 7., are formed onthe .ass plate as illustrated in lflCll. l,- Thc proportion of themodifying7 oxides in glass plate l is subsequently varied by carryingout an ion exchange process in ridge portions 3 from the surface of theglassdplatc fnl'igc'), NazO, iii-(30, RbO,

i CSEO, TlzU, AUZO, AggO, CagO, MgO, CaO, BaO, ZnO, CdO, Fbi), SnOg,LagOg, and the like may be employed as the modifying oxides.

Generally the refractive index of a substance is related to theniolecular refraction and the molecular volume inhercnt to thatsubstance. That is, the refractive index of the substance becomes largeras the molecular refraction becomes larger and as the molecular volumebecomes smaller. Here the molecular refraction is proportion to thepolarizability of the substance.

It is lrnown that the molecular refraction of glass can be approximatedby the sum of the individual ionic re fractions. Therefore, thequalitative etiect of the existence of a certain ion upon the refractiveindex of glass can be known by comparing the values of the electronicpolarizabilities per unit volume, or the values of Electronicpolarizability (Ionic radius)3 of the relevant ions. Representativepositive ions forming the modifying oxides, with respect to respectivemonovalent ions are those of lithium, sodium, potassium, rubidiurn,cesiurn, and thalliurn; the respective divalent ions are those ofmagnesium, calcium, strontium, barium, zine, cadmium` and lead; thetrivalent ion is that of lanthanum; and the tctravalent ion is that oftin. The values of the ionic radius, the electronic polarizability, andthe ratio of electronic polarizability to (ionic radius)3, are shown inTable 1. Since each ion has its inherent value of the ratio ofelectronic polarizability to (ionic radius)3, a. comparison can be madebetween the refractive index of glass containing positive ions formingthe modifying oxides and the refractive index of glass of the type inwhich a part or whole of the positive ions has a smaller value of thatratio than that of the first positive ions. That comparison indicatesthat the latter refractive index is smaller than the former refractiveindex.

TA B LE 1 Ionic Electr onie radius Electronic pol arizsbility Ion (A)polarizabilitfy tionie radius) 0. 78 0.03 O. 0632 0. J5 0.41 0. A78 1.33 l. 33 0. |65 1.49 1.98 0.509 l. 65 E. 31 0. 744 l. 49 2 1. 572 0. 78Jil 0. 20 0. 99 l 1. 13 1. 27 ti 0. 78 1. 43 5 0. S5 0. 83 8 1. 39 1. O38 1. 7l l. 32 7 2. l1 l. 22 l. Oi 5. GS O. 7st 3. 4 8. 85

Accordingly, by bringing a glass body containing certain i positive ionsforming the modifying oxides in contact with a salt. containing otherpositive ions which can form a modifying oxide having a different ratioof electronic polarizability to (ionic radius)3 from that of the firstpositive ions, it is possible to cause the first positive ions in theglass near its Contact surface to be exchanged by the positive ions inthe salt, and to make the refractive index of the glass decreaseapproaching the contact surface.

In this connection, it may be necessary to bring the glass body incontact with the salt and to heat the salt and the glass body so as tomaintain them at a tempera" ture at which the positive ions in the saltand the glass can diffuse within the glass body.

Therefore, in the fabrication of the optical device of FIG. i, if themodifying oxide in the glass plate ft is, for example, T120, then ridgeportions 3 of the glasi; tutti, is brought in contact with a salt ofi120, and ion exci'iange is carried ont between both of these oxides`whereby a refractive index gradient is formed i ihe ri portions 3.,

Body 4, having a sn'iaiier refractive indcr than that of said glassplate, is thereal;

joined to the 'naci'` surface of.

estarse (alight from going out of the glass plate. Body d may thus t/bemade either of silver, aluminum, gold, or the like, which (forms ametallic reflective mirror surface, or of a dielectric multi-layer lilm,with similar properties.

In addition, bore portions may bc selectively formed in the centralportion of optical lines 3, if necessary, and optical elements (forinstance, luminescent diodes, photoelectric elements, and the like) maybe disposed in those bore portions.

It is also possible, as shown in the embodiment of the inventionillustrated in FIG. 3, to establish a refractive index gradient in theportion of the glass plate near its rear surface, such that therefractive index of the glass plate decreases approaching that rearsurface, by bringing the rear surface of glass plate l in contact with asalt containing other positive ions which can form a modifying .A

oxide having a ditterent ratio of electronic polarizability to (ionicradius)3 from that of the positive ions forming the modifying oxide inglass plate t without providing body 4, and exchanging the positive ionsin the portion or" the glass plate near the Contact surface or the backsurface of the glass plate 1 by the positive ions in the salt.

According to this embodiment, since optical line 3 forms a focusingoptical transmitting body having a refractive index gradient asdescribed above in which the refractive index gradually decreases fromthe center axis towards the periphery, as shown in FIG. 3b this op ticaltransmitting line 3 has a more excellent optical trans missioncharacteristic than that of the first embodiment of FIG- l.

In the fabrication of the embodiment of FIG. 3, the step of performingion exchange from the back surface of glass plate may be carried outeither simultaneously with or separately from the step of performing ionexchange from the front surface of glass plate It to establish a desiredrefractive index gradient in ridge portions 3 (that is, the lighttransmitting lines). When both ion cxchange steps are carried outsimultaneously, there is an advantage that the working steps aresimplied. On the other hand, when the respective working steps arecarried out separately, there is another advantage that the temperature,time, and the like of the respective ion exchange Steps may beseparately controlled as desired.

In one practical process for fabricating the optical circuit of FIG. 3,a glass plate of about lOO microns in thickness was subjected to thephotoetching process to form a ridge of about l() microns in width andabout 30 microns in height. The surface of the glass plate including theridge is then brought into contact with a molten salt including T1250.,at a temperature of approximately 500 C. for a period of about l5 hours.This resulted in the desired gradient in the refractive indexdistribution in the portion of thc glass plate lying beneath the ridge.

FIG. 4 schematically illustrates the method for mam1- facturing a thirdembodiment ot' the present invention. At first, as shown in the planeand elevation views of FIGS. 4(a) and fidi) a mask t2 (for instance, laphoto-etching mask, a paraffin mask, etc.) is applied on the surface ofa glass plate tilt, according to the desired pattern of the opticallines to be formed on the glass plate.

Subsequently, as diagrammatically shown in FIG. Mc), the proportion orconcentration of the n'todifying oxides in glass plate is made to changeaccording to an ion exchange pr from the surface of a portion itl ofglass nlatc ii exposed through mask 32, to thereby form a i active.index gradient such that the refractive index decretses gradually fromthe surface of the exposed portion of glas;` pif-2te t towards its innerportion. This ion exchange proces` is carried out according to the sameprinciple as that escribcd above with respect to thc embodiment of ifil, LiOn, Nazi), lsLgO, ltbz), C320,

d T120, AuZO, Ag20, CazO, MgO, CaO, BaO, ZnO, CdCt, PbO, u02, LaZOE, andthe like, may be employed as the modifying oxides as before.

More particularly, glass plate il contains at least one or more kinds ofoxides among the above-referred modify ing oxides, and the ion exchangeis carried ont by bring tive ions which can form a modifying oxidehaving a larger value of electronic polarizability/(ionic radius)3 thanthe positive ions of the first modifying oxides.

Therefore, in the step illustrated in FIG. 4(6), if the modifying oxidein the glass plate 41 is H2O, then the exposed portion dit of glassplate 4i may be brought in contact with a salt of T to carry out ionexchange between both oxides.

Mask 452 is subsequently removed, and, thereafter the surface of. glassplate 4l is brought in contact with a salt of positive ions such as, forexample, KBO having a smaller value of electronic polarizability/(ionicradius) than the ions (for instance, TH) replaced in the glass plate 41through the preceding ion exchanvc step, to thereby form a refractive'index gradient such that the refractive index increases from thesurface of glass plate di towards its inner portion. As a result, theregion where the refractive index gradient was previously formed changesto a region where the refractive index decreases gradually from thecenter region having a larger refractive index radially outwardly, asdiagrammatically shown in FIG. lt-(a').

In one practical process for fabricating the embodiment of the inventionshown in FIG. 4, a glass plate having a thickness of approximately l mm.and coated with a metal film was subjected to photo-etching to form adesired strip of the etched-out portion of approximately 2O microns inwidth. The plate is then kept in contact with a molten salt containingTl2SO4 at a temperature of approximately 500 C. for a period of l5hours. This resulted in a gradient in the refractive index distributionthat decreases radially depthwise from the center of the etched-outportion (to the extent of 30 microns in the radial direction).

After the metal film mask was subsequently removed, the glass plate wasagain brought into contact with another molten salt containing KNO2 at atemperature of approximately 500 C. for a period of about l0 hours. Thisprocess decreased the refractive index at the etched` out portion to theextent that it becomes approximately equal to that of the glass plate,with the effect of the subsequent ion exchange decreasing toward thedeeper por`== tion of the glass plate. In this manner, the gradient inthe refractive index of glass plate 41 as shown in FIG. 4(d) isachieved.

In this way, an optical transmission line or lines in which therefractive index gradually varies along its transverse cross-sectionfrom the center towards the periphery, may be formed in glass plate Lt1according to a desired pattern of optical lines. Since this opticaltransmission line is provided with a refractive index distributionsimilar to the above-referred focussing light propagating body, it ispossible to transmit light through this optical transmisl sion line. Awiring plate for use in an optical circuit has thus been provided.

ln the embodiment of the invention shown in FIG. 5. after the mask i2has been removed subsequent to the completion of the first ion exchangeillustrated in FIG. 4(c'), a reflective mirro surface 5l may be formedon the surface of plate il without employing the second ion exchangestep as illustrated in FIG. 4M).

ln order to form reflective mirror surface Si, a g' plate having adifferent refractive index, a llif: tive film, a dielectric multi-layerfilm or the" n .ty be joined onto the surface of glass plate lil.According to `the embodiment illustrated in PIG. 5', although therefractive index gradient is not provided in proximity to the surface ofthe g`.ass, piate differently from they optik-air 9. The method m" cam6, in which said preparing step 3,083,123 of said rzmsparent dielectricbody inciudes the Step Of im 3,582,297 troducing into said dielectricbody at leas. one modifying 3,320,114 oxide. 3,563,057

19. The method of claim 9, in which said modifying 5 3,573,948 oxide isselected from the group consising of M02, N320, 3,647,406 R120, C320,T1201, A1120, f'xggo, C320, Cao, B30, ZBO, S1102 and M203.

- 3,556,640 References Ced 10 UNITED STATES PATENTS 3,542,536 11/1970Flam etal W 65-4 X 1,592,429 7/1926 Kraus 65 Digt Z 65-31, 60, Dig. 7

FRANK W. MIGA, Primary Examiner US. C1. XR.

